1. Field of the Invention
The present invention relates to a substrate forming mold usable in forming a resin substrate for use in, for example, optical disk, and a plate thickness adjusting method of formed substrate in a substrate forming mold.
2. Related Art of the Invention
Hitherto, resin materials have been used in forming of substrate of optical disk as memory medium. This substrate is formed by pouring and solidifying molten resin in a gap formed between a pair of molds, stable mold and movable mold, to be coupled together.
Conventionally, therefore, the plate thickness distribution of the formed substrate was determined by the processing precision of the member for forming the molds. However, as the memory capacity of the optical disk becomes larger, a higher precision is demanded in the plate thickness of the optical disk substrate. This is because the plate thickness of the substrate must be reduced in order to decrease the effect of tilt of the substrate.
Japanese Laid-open Patent No. 7-266378 discloses a method of disposing a shim between a junction member for forming a junction surface between a stable mold and a movable mold, and a mounting template for mounting it. In this case, since the cavity thickness varies, an outer ring for forming the outside diameter of the substrate is pressed to the stamper side by an elastic member.
A sectional view of this mold is shown in FIG. 19. A stable mold 101 and a movable mold 102 are tightened, and arrested and fixed by a fixed abutting ring 103 and a movable abutting ring 104. The fixed abutting ring 103 is fitted to a fixed mounting template 105 through a shim 106. In the fixed mounting template 105, a fixed mirror finished surface plate 107, a fixed bush 108, and a sprue bush 109 are provided sequentially toward the inner circumference. On the fixed mirror finished surface plate 107, a stamper 110 is held by a stamper holder 111 and an outer ring 112, respectively, on the inner circumference and outer circumference. The outer ring 112 is designed to move in cooperation with the movable mold 102, and is hence pressed to the stamper 110 side by a spring 113 which is an elastic member. At the movable mold 102 side, the movable abutting ring 104 is fastened to a movable mounting template 114 with bolts, and a movable mirror finished surface plate 115, a movable bush 116, an ejector punch 117, a cut punch 118, and an ejector pin 119 are disposed sequentially at the inner side. The fixed mirror finished surface plate 107 and movable mirror finished surface plate 115 are respectively provided with temperature adjusting grooves 120 and 121. The plate thickness of the formed substrate is adjusted by varying the plate thickness of the shim 106.
In such conventional method disclosed in Japanese Laid-open Patent No. 7-266378, however, a shim is disposed at the position for defining the thickness of the cavity formed between both molds when the stable mold and movable mold are joined together butt to butt. Accordingly, although the entire thickness can be adjusted in the formed substrate, but it is hard to suppress fluctuations in the plane of the formed substrate, that is, fluctuations of thickness in the radial direction or peripheral direction.
In consideration of such problems of the conventional mold, it is an object of the invention to present a mold for forming a substrate capable of suppressing fluctuations of thickness of the formed substrate, and a plate thickness adjusting method of formed substrate in the substrate forming mold.